diora-web/books/migrations/0005_progress_last_read_wins.py

from django.db import migrations, models


def keep_what_we_know(apps, schema_editor):
    """The continue point so far was the furthest place: it is that, and it was
    last saved at updated_at."""
    EBookProgress = apps.get_model('books', 'EBookProgress')
    for p in EBookProgress.objects.all().iterator():
        p.furthest_fraction = p.scroll_fraction
        p.furthest_anchor = p.position_anchor
        p.read_at = int(p.updated_at.timestamp() * 1000)
        p.save(update_fields=['furthest_fraction', 'furthest_anchor', 'read_at'])


class Migration(migrations.Migration):

    dependencies = [
        ('books', '0004_ebook_is_read'),
    ]

    operations = [
        migrations.AddField(
            model_name='ebookprogress',
            name='read_at',
            field=models.BigIntegerField(blank=True, null=True),
        ),
        migrations.AddField(
            model_name='ebookprogress',
            name='device',
            field=models.CharField(blank=True, default='', max_length=40),
        ),
        migrations.AddField(
            model_name='ebookprogress',
            name='furthest_fraction',
            field=models.FloatField(default=0.0),
        ),
        migrations.AddField(
            model_name='ebookprogress',
            name='furthest_anchor',
            field=models.CharField(blank=True, default='', max_length=30),
        ),
        migrations.RunPython(keep_what_we_know, migrations.RunPython.noop),
    ]